An apparatus, such as a facsimile, a copying machine, and a scanner, is equipped with a document reading apparatus, which reads characters and image information from a face of a document by light reflected from the document face. The document reading apparatus is equipped with an illuminating device, which illuminates the document face. Such an illuminating device comprises of two rod-shaped light guides, which are arranged to be aligned with each other, and light emitting elements, which are provided at an end face of each of the two light guides. The end faces, at which the light emitting element for one of the light guides and the light emitting element for the other light guide are arranged, face opposite directions (see Japanese Patent Application Publication No. 2001-268320).
FIG. 13 is an explanatory cross sectional view of the structure of a main part of a document reading apparatus equipped with an illuminating device of the background art. In this figure, an illuminating device 80 has two rod shape light guides 81 and 82, which respectively extend in a main scanning direction (a direction perpendicular to the figure) and a chassis 83 for holding these light guides 81 and 82. A light emitting element (not shown in the figure) is arranged at one end face of the light guide 81, which is one of the two light guides 81 and 82 (for example, an end face in a near side of the figure), and another light emitting element (not shown in the figure) is arranged at the other end face of the other light guide 82, that is, an end face that faces in a direction opposite to the direction that the end face of the light guide 81 faces. The light guides 81 and 82 have light emitting faces 81a and 82a respectively. A platen 90 (contact glass), on which a document is placed, is provided above the illuminating device 80. A document having a document face 91 is placed on the document stand 90. A photoelectric conversion element 95 receives document reflection light, which is reflected from the document face 91, through a rod lens array 96. The photoelectric conversion element 95 is provided on the substrate 97.
In the illuminating device 80, the light emitted from the light emitting elements enters the light guides 81 and 82 from the end faces and is guided by the light guides 81 and 82 in the main scanning direction. When the light that is emitted from the light guides 81 and 82 irradiates the document face 91, a belt-like effective lighting area for reading the information of the document face, which extends in the main scanning direction, is formed on the document face 91, and the photoelectric conversion element 95 receives the document reflection light reflected from the effective lighting area of the document face 91 through the rod lens array 96. Character and image information in the document face are read by relatively moving the effective illumination area with respect to the document face 91 in a subscanning direction, that is, a direction perpendicular to a longitudinal direction of the light guides. Here, the effective illumination area is an illumination area, which receives 95% or more of a predetermined illuminance, which is, for example, the maximum illuminance. In the illuminating device, it is important that the effective illumination area has a certain width, which is required to read the information in the subscanning direction, for example, width of ±3 mm or more from the center position of the effective illumination area (6 mm as the width of the effective illumination area) and has high uniformity of irradiance distribution in the subscanning direction.
Therefore, it can be said that in the illuminating device 80 the light emitting elements are arranged at end faces of the two light guides, which face in opposite directions, so that the effective illumination area, which has high uniformity of irradiance distribution, can be obtained by superimposing light from the light guide 81 and the light guide 82, since the irradiance distribution of light emitted from the light guide 81 and that of light emitted from the light guide 82 are symmetrical on the document face. However, in the illuminating device 80, although it is possible to obtain the effective illumination area, which has high uniformity of irradiance distribution in the main scanning direction, it is difficult to obtain the effective illumination area, which has width required to read information on a document face in the subscanning direction, and which has high uniformity of irradiance distribution in the subscanning direction.